The pathways and machanisms of transepithelial transport of chloride ions are being investigated in the proximal tubule of the Neuturus kidney. Chloride sensitive intracellular micro-electrodes were constructed to monitor intracellular chloride activity and to determine cellular responsiveness to change extracellular chloride concentration. Tracer chloride fluxes across the tubule were measured to quantitate the chloride movements across the tubule cells and through the shunt pathway.